High powered duplexing arrangement



T. E- MANWARREN HIGH POWERED DUPLEXING ARRANGEMENT Jan. 29, 1963 2Sheets-Sheet 1 Filed June 29. 1959 SWITCHING CIRCUIT NO A.

, THOMAS E. MANZWARRE FIGJA.

ins ATTORNEY.

Jan. 29, 1963 T. E. MANWARREN HIGH POWERED DUPLEXING ARRANGEMENT FiledJune 29. 1959 .2 Sheets-Sheet 2 INVENTORI THOMAS E. MANWARREN HISATTORNEY.

United States Patent HIGH POWERED DUPLEXKNG ARRANGEMENT Thomas E.Manwarren, Fernwood, FLY assignor to General Electric Company, acorporation of New York Filed June 29, 1959, Ser. No. 823,393 2 Claims.(Cl. 333-$3) This invention relates generally to the transmission andreception of electromagnetic waves and more particularly to a method andmeans for automatically and selectively switching waves of high and lowpower level to predetermined circuits. Reference can be made to Patent2,408,055 issued to M. D. Fiske on September 24, 1946 for a detaileddescription of the manner in which a duplexing arrangement functions toswitch electromagnetic waves between various load circuits.

In effecting the propagation of electromagnetic Waves along wave guidingstructures such as waveguides, coaxial lines, etc., it is oftentimesdesirable to selectively switch waves of different power to respectiveload circuits. For example, in the field of radar obstacle detection itis a common practice to operate the pulse transmitter and the pulse echoreceiver in conjunction with a common antenna. By providing a waveguideswitch in a section of the waveguide feeding the antenna which is commonto both the transmitter and the receiver, it is possible to limitsubstantially all the transmitted energy to the antenna and all thereceived energy to the receiver with an acceptable minimum ofinterchange of energy between the transmitter and receiver. If theswitching apparatus were made non-linear, that is, dependent upon theintensity of applied wave energy, then an automatic switching circuitresults.

* It is an object of the present invention to provide an improved methodfor operating a transmitter into and a receiver from a common antennasystem.

A further object of the invention is to provide an improvedtransmit-receive switching device which can etiectively handle a largeramount of power from a transmitter than heretofore possible.

It is another object of my invention to provide a novel method and meansforselectively routing electromagnetic waves of difierent energyintensity into separate channels.

It is another object of my invention to provide a method and means forautomatically changing the impedance of an electrical network inaccordance with the intensity level of propagated waves to eiiectswitching of said waves in a desired manner.

It is a further object of my invention to provide an improved signalprocessing arrangement.

The novel features which are believed to be characteristic of myinvention are set forth with particularity in the appended claims. Myinvention itself, however, both as to its organization and method ofoperation, together with other objects and advantages thereof, may bestbe understood by reference to the following description taken inconnection with the accompanying drawings in which:

FIGS. la, lb and 1c illustrate schematically wave energy switching in anelectrical network employing an ionizable medium;

FIG. 2 illustrates schematically an embodiment of the 3,7h,i5? PatentedFan. 29, fi ht;

invention wherein an ionizable medium in series with a capacitivereactance constitutes a switching network;

FIG. 3 illustrates schematically an embodiment of the invention whereinthe ionizable medium is physically located outside the waveguidestructure wherein electrical waves are to be controlled; and

FIG. 4 illustrates schematically a circuit network arrangement in whicha reactance is placed in parallel with an ionizable medium for eifectingcontrol of waves propagated in a waveguide.

Referring to FIG. 1 there is shown an arrangement involving circuits 1,2 and 3. In a particular application it is desired to selectivelycommunicate electromagnetic waves between various combinations of thecircuits while preventing the communication of waves between othercombinations of these circuits. To efiect this control there is provideda switching circuit 4 which couples the various circuits 1, 2 and 3 bymeans of waveguide sections 5, 6 and 7. In a specific embodiment,circuit 1 might comprise a radar transmitter which transmits highpowered pulses of electromagnetic energy at a particular recurrencerate. It is desired to couple these high powered transmitter pulses to aload circuit 2 which might comprise an antenna for radiating the highfrequency energy out into space. In effecting the coupling of highpowered pulses from circuit 1 to circuit 2, it is desired to prevent thecoupling of high powered pulses into circuit 3 which might comprise areceiver for receiving the relatively weak echo pulses returned from aremote object which has been illuminated by the transmitted pulses.After a predetermined interval of time dependent upon the distance fromthe antenna 2 to the illuminated object, a weak echo pulse is receivedin antenna 2 and it is a function of the switch 4 to couple the weakpulse over waveguide sections 6 and 7 to the receiver 3 while preventingthe coupling of the weak pulses to the transmitter by way of waveguidesection 5. This switching action is commonly referred to as duplexingwherein high intensity pulses and low intensity pulses are coupled todifferent channels. It is the function of the switching circuit 4 torespond automatically to the intensity or" the wave being propagatedbetween the waveguide sections 5, 6 and 7 to eifect the properswitching.

Referring to FIG. lb, there is shown in accordance with one embodimentof the invention a switching arrangement for use in a section ofrectangular waveguide ti. FZG. lb is a cross-section view through aresonant cavity formed in part by the Walls of waveguide 8 with aswitching network included therein comprising electrically conductiveposts 9 and is coupled by an ionizable medium it. The circuitscomprising 9, it} and iii are connected in series with the distributedcapacity, shown as 12, formed between the post it} and the waveguidewalls. The ionizable medium may comprise an enclosed vessel formed of adielectric wall material 13 containing an ionizable gas such as argon,neon, crypton, Zenon, etc. Under normal conditions with no or littlewave energy being propagated through the cavity, the gas is non-ionizedand the electrical circuit comprising 9, it 11 and 12 has a firstimpedance value aiiecting control of the waves propagated through thecavity in one manner. In response to the intensity of waves propagatedin the cavity above a predetermined level, the ionizable gas responds tobecome ionized and effect a change in the impedance value of theelectrical circuit comprising elements 9, 1t), 11 and 12 to effectcontrol of the waves propagated in the cavity 3 in a manner differentfrom said first manner. in the nonconducting, non-ionizable state theposts 9 and 1t; are effectively connected to one another only by thehigh capacitive reactance of the gap between the posts. When the gas isionized, a virtual short circuit ioins the elements 9 and 19 together.However, all current which flows through the ionized medium 11 must alsohow through the series reactance 12 and, therefore, the magnitude ofcurrent is reduced. This accomplishment effectively increases the powerhandling capacity of the duplexer.

Reference is now made to PEG. 1c wherein the functioning of theswitching network shown in lb is illustrated in greater detail. Whereverpossible, common reference numerals have been retained in FIG. is toagree with those used in FIG. lb and 1a. Actually, two electricalswitching component networks, shown as 14 and 15, are employed in thearrangement of FIG. 1c. It should be noted that the resonant cavitiesare shown as being formed of rectangular waveguide sections with inputand output coupling susceptances 16, 17 and 18. Briefly, thesesusceptances comprise conductive walls introduced at the junction ofwaveguides 5, 6 and 7 with the resonant cavities. Before describing thefunctioning of the arrangement of FIG. 10, it may be well to considerfor a moment the functioning of a cavity resonator which is coupled to awave guiding structure. Briefly, the input impedance of the resonantcavity approximates very closely at short circuit when the resonantcavity is detuned from the operating frequency of the waves beingpropagated therethrough, thereby blocking passing of waves through thecavity. If the resonant cavity is tuned to the operating frequency ofthe waves being propagated therethrough, wave energy is permitted to bepassed through the cavity resonator. This effectively constitutes anunblocked condition of the cavity.

in the arrangement of FIG. 10, the electrical switching networks havebeen dimensioned such that when electromagnetic waves are beingpropagated with an intensity below a predetermined intensity level, orwaves of the relatively low intensity level of reflected echoes, thecavity resonators are tuned to the system operating frequency. Assumingthe tuned status of the resonators 14 and 15, we shall now describe acycle of events illustrating the functioning of the switching circuitsto provide the desired coupling of high and low intensity waves.Assuming circuit 1 is a generator of high powered pulses of megawattintensity, these high powered radar pulses are transmitted overwaveguide section through the switching circuit 4-, the waveguidesection 6 to circuit 2 which might comprise a radar antenna for beamingthe energy out to a remote object. A portion of the high powered pulsebeing communicated to the antenna 2 is coupled into the resonantcavities 14 and 15. Both cavities respond by having their ionizablemediums become ionized and effectively detune the cavity resonators withthe help of the distributed capacity 12 and the conductive posts 9 and10, shown in FIG. 1b. This detuning of the cavities results in aneffective short circuit being exhibited at the cavity input ports acrossthe susceptance walls 16 and 17. Thus very little wave energy is coupledto the load circuit 3, which might comprise the receiver. In eifect,high powered pulses from circuit 1 are coupled to circuit 2 withsubstantially no electromagnetic reflections occurring in the intermediate waveguide couplings.

The transmitted pulse is reradiated from a remote object as a so-calledecho pulse. This echo pulse of relatively low intensity of the order ofmicrowatts is received at the circuit 2 which might comprise the sameantenna. it is desired to couple this weak echo pulse to the receivergirc it-3 without losing any of the energy by coupling into thetransmitter circuit 1. At the conclusion of the transmitted pulse, theionizable mediums in cavities 14 and 15 become de-ionized, and returnthe cavities to their tuned condition. As previously mentioned, in thetuned condition waves are coupled through the cavity 15 to circuit 3. Tooptimize coupling, the impedance of circuit 3 is matched with theimpedance of the circuit feeding it. In the case of cavity 14, the shortcircuiting wall at 19 reflects an impedance at the input ports to cavity14, which in combination with the susceptance 16 presents an effectiveopen circuit at the junction of the main waveguide wall and the cavity14. The open circuit exhibited at the input port to the cavity 14refiects an effective short circuit across the waveguide section 5feeding the transmitter located at circuit 1, thus preventing lowintensity echoes from being absorbed in the transmitter circuit. Thewaveguide and cavity structure is dimensioned such that the shortcircuit across the transmitter waveguide feed 5 is reflected as a shortcircuit across the waveguide sections connecting 5 and 6 such that theecho pulses are etfectively all communicated to the resonator 15. Thecavity resonator 15 is coupled by means of a waveguide section 7 to theload circuit or receiver 3. As previously mentioned, the characteristicsof the resonant cavity 15 are such that in the tuned condition itexhibits at its input port effectively the impedance of the receiverwhich is coupled to the output port of the cavity resonator.Accordingly, practically all of the input echoes are coupled to thereceiver and little of the received energy is lost in the remainingcircuitry of the system shown.

Referring to FIG. 2, there is shown a further embodiment of anelectrical switching network wherein the ionizable medium comprisesessentially the only coupling to the distributed capacity 20. Theionizable medium 2 1 comprises effectively a vessel having a wallportion formed of a dielectric material 22 such as glass or ceramic andcontaining the gases, argon, neon, etc., previously mentioned. Theionizable medium has the wall material 22 cemented to a conductive plate23 which can form a part of the wall of the cavity resonator 24. Thecavity resonator normally has one particular tuning in the conditionwhere ionizable medium is not ionized and upon ionization in response towaves propagated in the cavity above a predetermined intensity themedium becomes ionized and efiectively exhibits properties of anelectrically conductive post for the distance L. This effectiveconductive post, together with the distributed capacity 20, operates toalter the tuning of the cavity resonator such that the electricalswitching network comprising 2%, 21, 22 and 23 controls the waves in adifferent manner than in the condition when the medium is un-ionized andeffectively is out of the circuit. The current which flows through theionized medium 21 also flows through the series reactance 2%. Therefore,the magnitude of this current is reduced, thereby effectively increasingthe power handling capacity of the duplexer.

Referring to FIG. 3, the ionizable medium 25 is contained in a vesselformed by a dielectric wall portion 26 and an electrically conductivewall portion 27 which may comprise steel, copper, or some other suitableelectrically conductive material. In a preferred embodiment, the vesselwas in the form of a cylinder with an electrically conductive post 28conductively connected to the wall material 27 at one end and protrudinginto the cavity resonator through the walls 29. The post can be formedof any suitable electrically conductive material, such as metal. In itsnon-ionized state the electrical switching circuit comprises an annulus31 formed of a conductive material, such as metal, which is concentricwith the post 23 and spaced on its inner diameter therefrom andelectrically conductively connected to the wall portions 27 at the outerperiphery thereof.

The operation of the circuit of FIG. 3 is as follows:

The switching circuit is composed of the series combina- 30, theconducting tion of the distributed capacitance post for the length L,and the into the coaxial section at the impedance seen looking into thedielectric window is composed of a combination of reactances formed inthe coaxial transmission line of length L +L in combination with thecapacitive reactance of the annular disk 31.

During the application of power levels below those necessary to causeionization of the gas 25, the short circuited coaxial transmission lineof length L places an inductive impedance at the annular disk which isof the same magnitude but opposite in sign to the capacitive reactanceof the disk. As a result, the impedance at the disk being made up of twocancelling reactances in parallel is effectively an open circuit. Thisopen circuit is seen as some reactance Z at the input window in thecoaxial section.

impedance Z seen looking dielectric window 26. The

During the application of power levels high enough to cause ionizationof the gas 25, a discharge forms at the gap between the annular disk 31and the center conductor 28. As a result, a virtual short circuit isplaced at the annular gap and is reflected as an impedance Z at theinput window of the coaxial line. The impedance at the annular disk hasthus been changed from an open circuit during the application of lowlevel energy to that of a short circuit for incident electromagneticenergy of a magnitude sufiicient to cause ionization of the gas. Due tothe characteristics of transmission lines and waveguides, the impedancesZ and Z seen at the input window to the coaxial section are relatedessentially by the equation Z =l/Z It is this change in the impedance Zwhich constitutes the switching action necessary for detuning the cavityin which the circuit of FIG. 3 is placed. Reactance 30 decreases thecurrent flow on inductor 28 and consequently also the current throughthe glow discharge region. As a result, the power handling capacity ofthe duplexer is increased.

Referring to FIG. 4, there is shown a switching network which iscomposed of an inductive post 32, a dielectric cylinder 33 containing anionizable medium 34 placed in a rectangular waveguide 35. During theapplication of electromagnetic energy below the value necessary to causeionization of the gas, the network is composed essentially of theinductive post 32. At incident levels of energy of a magnitude greatenough to cause ionization of the gas 34, the efiective diameter of thepost is increased and the reactance of the switching circuit isdecreased. After ionization of the gas medium, the circuit is composedof the inductive post 32 in parallel with the ionized medium 34. Thechange in reactance of the switching circuit for power levels above thevalue necessary for ionization of the gas column elfectively detunes thecavity in which the circuit is placed. The inductive post in parallelwith the glow discharge carries part of the current flow and thereforeless current flows through the discharge region than without theparallel reactance of the post. As a result, the power handling capacityof the duplexer is increased.

While a specific embodiment has been shown and described, it will ofcourse be understood that various modifications may yet be devised bythose skilled in the art which will embody the principles of theinvention and found in the true spirit and scope thereof.

What I claim and desire to secure by Letters Patent of the United Statesis:

1. In combination, a cavity resonator comprising a wave guide having twobroad walls and two narrow walls, a non-linear switching circuitcomprising a chamber containing an ionizable medium connected to one ofsaid broad walls and extending in length only partially toward the otherof said broad walls, said medium being ionizable in response toelectromagnetic waves above a predetermined level to de-tune saidresonant cavity and to provide a fixed impedance element seriallyconnecting said medium across said broad walls to limit current flowingthrough said medium to non-destructive values during ionization, saidionizable medium providing the only path through said chamber in adirection from one broad wall to the other broad wall whereby aconductive path exists only when the intensity of said electromagneticwaves is above said predetermined level.

2. In combination, a cavity resonator tuned for propagatingelectromagnetic waves of a given frequency, an electrical circuitcomprising a chamber containing an ionizable medium connected to one ofa pair of walls of said cavity resonator, said medium being ionizable inresponse to electromagnetic waves above a predetermined level to de-tunesaid resonant cavity sufficiently to prevent the propagation of waveenergy and to provide a fixed impedance element serially connecting saidmedium across said pair of walls of said cavity resonator to limitcurrent flow through said medium to nondestructive values duringionization, said ionizable medium providing the only path through saidchamber in a direction from one of said pair of walls to the otherwhereby a conductive path exists only when the intensity of said appliedwave energy is above said predetermined level.

References Cited in the file of this patent UNITED STATES PATENTS2,408,055 Fiske Sept. 24, 1946 2,522,861 Cork Sept. 19, 1950 2,632,854Altar et a1 Mar. 24, 1953 2,765,445 Zaleski Oct. 2, 1956

1. IN COMBINATION, A CAVITY RESONATOR COMPRISING A WAVE GUIDE HAVING TWO BROAD WALLS AND TWO NARROW WALLS, A NON-LINEAR SWITCHING CIRCUIT COMPRISING A CHAMBER CONTAINING AN IONIZABLE MEDIUM CONNECTED TO ONE OF SAID BROAD WALLS AND EXTENDING IN LENGTH ONLY PARTIALLY TOWARD THE OTHER OF SAID BROAD WALLS, SAID MEDIUM BEING IONIZABLE IN RESPONSE TO ELECTROMAGNETIC WAVES ABOVE A PREDETERMINED LEVEL TO DE-TUNE SAID RESONANT CAVITY AND TO PROVIDE A FIXED IMPEDANCE ELEMENT SERIALLY CONNECTING SAID MEDIUM ACROSS SAID BROAD WALLS TO LIMIT CURRENT FLOWING THROUGH SAID MEDIUM TO NON-DESTRUCTIVE VALUES DURING IONIZATION, SAID IONIZABLE MEDIUM PROVIDING THE ONLY PATH THROUGH SAID CHAMBER IN A DIRECTION FROM ONE BROAD WALL TO THE OTHER BROAD WALL WHEREBY A CONDUCTIVE PATH EXISTS ONLY WHEN THE INTENSITY OF SAID ELECTROMAGNETIC WAVES IS ABOVE SAID PREDETERMINED LEVEL. 